Recurrence of galactic cosmic-ray intensity and anisotropy in solar minima 23/24 and 24/25 observed by ACE/CRIS, STEREO, SOHO/EPHIN and neutron monitors

Abstract

Aims. We studied the 27-day variations of galactic cosmic rays (GCRs) based on neutron monitor (NM), ACE/CRIS, STEREO, and SOHO/EPHIN measurements in the solar minima 23/24 and 24/25, which are characterized by the opposite polarities of solar magnetic cycle. We used the opportunity to reanalyze the polarity dependence of the amplitudes of the recurrent GCR variations in 2007–2009 for the negative A < 0 solar magnetic polarity and to compared it with the clear periodic variations related to solar rotation in 2017–2019 for positive A > 0. Methods. We used the Fourier analysis method to study the periodicity in the GCR fluxes. Because the GCR recurrence is a consequence of solar rotation, we analyzed not only GCR fluxes, but also solar and heliospheric parameters to examine the relations of the 27-day GCR variations and heliospheric as well as solar wind parameters. Results. We find that the polarity dependence of the amplitudes of the 27-day variations of the GCR intensity and anisotropy for NMs data is kept for the last two solar minima: 23/24 (2007–2009) and 24/25 (2017–2019), with greater amplitudes in the positive A > 0 solar magnetic polarity. ACE/CRIS, SOHO/EPHIN, and STEREO measurements are not governed by this principle of greater amplitudes in the positive A > 0 polarity. The GCR recurrence caused by the solar rotation for low-energy (< 1 GeV) cosmic rays is more sensitive to the enhanced diffusion effects, resulting in the same level in 27-day amplitudes for the positive and negative polarities. In contrast, the high-energy (> 1 GeV) cosmic rays that are registered by NMs are more sensitive to the large-scale drift effect, which leads to the 22-year Hale cycle in the 27-day GCR variation, with the larger amplitudes in the A > 0 polarity than in A < 0.

Galactic Cosmic Rays Throughout the Heliosphere and in the Very Local Interstellar Medium

“…As first observed in 1938, recurrent variations with a period of 27 days, corresponding to the synodic solar rotation and at multiple of that frequency (e.g. periods of 13.5 and 9 days) are related to the passage of corotating interaction regions originating from one or more coronal holes of the Sun (Modzelewska and Gil 2021 ). Until the AMS measurements the general idea was that the strength of the periodicity steadily decreases with increasing rigidity of cosmic rays, differently in solar maximum and minimum (Gil and Alania 2013 ).…”

Advancing Precision Particle Background Estimation for Future X-Ray Missions: Correlated Variability between the Alpha Magnetic Spectrometer and Chandra/XMM-Newton

“…This modulation of GCR flux leads to a range of quasiperiodic variations occurring on various timescales, spanning from hours to several years. These phenomena have been extensively studied in Usoskin (2017), Kudela & Sabbah (2016), Chowdhury et al (2016), Bazilevskaya et al (2014), Modzelewska & Gil (2021), and references therein.…”

Precision Measurement of Daily Proton and Helium Fluxes by the Alpha Magnetic Spectrometer

“…The nonrecurrent variations are mainly due to the interactions of cosmic rays with strong transient disturbances in the interplanetary magnetic field, such as shock waves generated by interplanetary coronal mass ejections, especially during solar maxima, that can last from days to weeks [5]. Recurrent variations with a period of 27 days, corresponding to the synodic solar rotation, and at multiples of that frequency (e.g., periods of 13.5 and 9 days) are related to the passage of corotating interaction regions originating from one or more coronal holes of the Sun [6][7][8][9][10][11][12][13][14], as first observed in 1938 [15]. Previous studies on the estimated rigidity dependence in periodicities, for example in Ref.…”